import math

a  = int(input("输入边长a:"))
b  = int(input("输入边长b:"))
c  = int(input("输入边长c:"))

p = (a+b+c)/2

s = math.sqrt(p*(p-a)*(p-b)*(p-c))

print("三角形面积是：",round(s,2))

